1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine using an electrophotographic process.
2. Description of Prior Art
For an image forming apparatus such as a copying machine using an electrophotographic process, it is desirable to reproduce an image of the same density for the same image data. In order to reproduce an image of stabilized density on a paper, it is known to form a standard toner image. When a copy operation is started or when a predetermined mode is set, a standard toner image is formed on a photoconductor, and the transfer efficiency of the toner image onto the paper is detected. Then, development or transfer conditions are controlled according to the detected results.
However, the above-mentioned stabilization is not controlled appropriately in cases, for example, when toners are deteriorated or when the resistance of a paper on which a toner image is transferred becomes lower than expected by absorbing water content from the humidity of ambient environment. Even if toners have been charged normally, they are charged with the reverse polarity at a transfer section in a copying machine, and the amount of toners remaining on the photoconductor increases after passing the transfer section in the copying machine, so that the transfer efficiency becomes worse. Further, if toners are deteriorated, the amount of charges of toners after development and before transfer becomes lower. Toners are also charged with the reverse polarity at the transfer section in this case, so that the transfer efficiency becomes worse.